1. Field of the Invention
This invention relates generally to methods and apparatus for forming joints along treads, and in particular instances, joining tire tread portions to form joined tire treads, such as tread rings, for tire manufacturing operations.
2. Description of the Related Art
It is known to apply treads to new and used tire carcasses. Treads are applied to green tire carcasses in new tire manufacturing operations. Treads are also applied to used tire carcasses during tire retreading operations. In retreading operations, for example, treads may be formed and joined to form a ring about the tire carcass.
Current retreading methods include arranging elastomeric material between opposing ends of the tread and filling a gap between the ends to form the joint. In such instances, the opposing tread ends may be stapled together to maintain the ends in a closed arrangement for curing operations. The retreaded tires are then inserted into a flexible curing membrane and cured under vacuum pressure in a curing vessel. Subsequently the staples are removed. The resulting tread joint is often readily noticeable to an observer. This is in part because the joint comprises a noticeable gap filled with elastomeric material that is generally unconstrained during the curing process, whereby an uneven or non-smooth joint is formed. Further, the cured tread typically includes markings indicating the prior use of staples.
A current splice joint method may also be employed to join treads, whereby ends of a tread are joined by placing elastomeric joining material between the tread ends and subsequently placing the joined tread into a flat mold. In such methods, the tread joint is simply encapsulated by the mold and formed by pressure generated by compressing the tread joint within the mold. Because the mold is a typical mold used to originally form the tread, no unique features are provided for the joining operations, and therefore, joining material is unable to escape the mold. Therefore, any excess joining material is consumed and molded into the tread, which creates an oversized portion of the tread. Accordingly, the resulting tread joint may not be aesthetically pleasing as it varies is size and shape from the remaining portions of the tread. This is due to the inability to sufficiently control the formation of the joint.
Another current method of retreading includes forming a jointless, continuous tread ring using a molding process. The ring is then applied to the tire carcass and cured in a curing membrane within a curing vessel. Because the tread is free of any joint, this method provides an aesthetically pleasing tread. However, because this method employs a tread ring mold, the method can be very costly.
Accordingly, there is a need to provide a joined tread ring that is similar in cosmetic quality to molded tread rings by employing improved tread splicing methods and apparatus without the excessive costs associated with tread ring molds.